Mapping the Cosmic Microwave Background Anisotropy:The First Flight of the QMAP Experiment

We report on the first flight of the balloon-borne QMAP experiment. The experiment is designed to make a map of the cosmic microwave background (CMB) anisotropy on angular scales from 0.70d to several degrees. Using the map, we determine the angular power spectrum of the anisotropy in multipole bands from l~40 to l~140. The results are consistent with the SK (from Saskatoon, Saskatchewan, Canada) measurements. The frequency spectral index (measured at low l) is consistent with that of CMB and inconsistent with either Galactic synchrotron or free-free emission. The instrument, measurement, analysis of the angular power spectrum, and possible systematic errors are discussed.